1. Conversion: 12 slices = one pizza
BELLWORK 8/18/16
Suppose there are 12 slices of pizza in one pizza. How many slices are in 7 pizzas?
Given: 7 pizzas
Want: # of slices
Conversion: 12 slices = one pizza

2. Solution
Check your work…
84 slices
7 pizzas 1
12 slices
1 pizza X =

3. Dimensional Analysis
The systematic method of converting from one unit to another.
Why is dimensional analysis important?

4. Dimensional Analysis

5. How Does Dimensional Analysis Work?
A conversion factor is used, along with what you’re given, to determine what the new unit will be.

6. How Does Dimensional Analysis Work?
If we write these expressions mathematically, they would look like
3 cm = 50 km

7. Examples of Conversion Factors
60 s = 1 min
60 min = 1 h
24 h = 1 day

8. Examples of Conversions
You can write any conversion factors as fractions.
For example, you can write:
60 s = 1 min
as 60s or 1 min
1 min s

9. Examples of Conversions
Again, just be careful how you write the fraction.
The fraction must be written so that like units cancel.

10. Steps Start with the given value. Write the multiplication symbol.
Choose the appropriate conversion factor.
The problem is solved by multiplying the given data & their units by the appropriate unit factors so that the desired units remain.
Remember, cancel like units.

11. Conversion: 365 days = one year
Learning Check #1
2. How old are you in days?
Given: 17 years
Want: # of days
Conversion: 365 days = one year

12. Solution
Check your work…
6052 days
17 years 1
365 days
1 year X =

13. Conversion: 2.54 cm = one inch
Learning Check #2
3. There are 2.54 cm in one inch. How many inches are in 17.3 cm?
Given: 17.3 cm
Want: # of inches
Conversion: 2.54 cm = one inch

14. Be careful!!! The fraction bar means divide.
Solution
Check your work…
6.81 inches
17.3 cm 1
1 inch
2.54 cm X =
Be careful!!! The fraction bar means divide.

15. Multiple-Step Problems
Most problems are not simple one-step solutions. Sometimes, you will have to perform multiple conversions.
Example: How old are you in hours?
Given: 17 years
Want: # of days
Conversion #1: 365 days = one year
Conversion #2: 24 hours = one day

16. Solution Check your work… 17 years 1 365 days 1 year 24 hours 1 day X=
148,920 hours

17. Jabberwocky Work on this problem individually. Show all of your work.
Turn in your answer to me

18. Combination Units
Dimensional Analysis can also be used for combination units.
Like converting km/h into cm/s.
Write the fraction in a “clean” manner:
km/h becomes km h

19. Combination Units Example: Convert 0.083 km/h into m/s.
Given: km/h
Want: # m/s
Conversion #1: 1000 m = 1 km
Conversion #2: 1 hour = 60 minutes
Conversion #3: 1 minute = 60 seconds

20. Solution Check your work… 83 m 1 hour 0.083 km 1 hour 1000 m 1 km X =
60 min
1 min
60 sec = X X
0.023 m
sec

21. Crash of Flight 143
Watch this video and answer the following questions.
1. What was the cause of the Crash of Flight 143?
2. How does this relate to the importance of using dimensional analysis?